Internal combustion engines for vehicles, such as motor vehicles, are available in many different configurations, which may include different numbers and arrangements of cylinders, the cylinders having different ignition timings and/or ignition orders. Some engine configurations may lead to inherent imbalances in the forces exerted on the crank shaft of the engine during engine running. This can lead to reciprocating, rocking, or torsional vibrations of the crank shaft and/or engine.
Depending on the configuration of the engine, the vibrations may be first order, second order or higher order vibrations relative to the rotation of the engine crank shaft. Again, depending on the configuration of the engine, the severity of the vibrations may vary according to the running speed of the engine.
Many engines incorporate one or more balance shafts, comprising out-of-balance weights, which are driven by the engine to balance vibrations. The balance shafts are typically provided within a housing of the engine and may be adequately supported and lubricated by the engine. The balance shafts may be mechanically coupled to the engine crank shaft via a gear or chain drive such that they may be driven synchronously with the crank shaft of the engine.
In order to reduce the fuel consumption of a motor vehicle, the motor vehicle may be provided with a variable displacement engine, which is capable of deactivating one or more cylinders of the engine when the torque being delivered by the engine or the running speed of the engine is below a threshold value. For example, for an engine assembly comprising four cylinders, it may be desirable to deactivate two of the cylinders when the engine is running at or below a threshold running speed in order to improve the fuel consumption of the vehicle.
Deactivating one or more cylinders of the engine affects the balance in the forces being exerted on the crank shaft during operation of the engine assembly, which may affect the order and/or mode of vibrations of the crank shaft and/or engine and as a result the vibrations may not be balanced.
In one example, the issues described above may be addressed by an internal combustion engine assembly for a motor vehicle comprising an engine, an electric motor wherein the motor vehicle is a hybrid vehicle and wherein the electric motor forms part of a hybrid drive system of the vehicle, and a balance shaft comprising an eccentric mass, wherein the electric motor is configured to selectively rotate the balance shaft in order to balance a vibration characteristic of the engine.
The balance shaft may be provided on the engine. For example, the balance shaft may be provided within a housing of the engine and may be supported, e.g. rotatably supported, by the housing. Alternatively, the balance shaft may be coupled to the engine, e.g. to the engine housing. The balance shaft may be elongate and may extend in a direction parallel to a longitudinal axis of the engine. The balance shaft may comprise a plurality of eccentric masses arranged along the length of the balance shaft, e.g. at or towards each end of the balance shaft. In other arrangements, the balance shaft may consist of the eccentric mass.
The electric motor may be configured to selectively provide power to an engine crank shaft or transmission of the motor vehicle, e.g. to supplement power from the internal combustion engine.
The engine may be a variable displacement engine, e.g. configured to selectively deactivate one or more cylinders of the engine. The vibration characteristic of the engine may vary according to the displacement of the engine.
The engine assembly may be configured to control the rotation of the balance shaft according to the displacement of the engine. The rotational speed and/or direction of the electric motor may be variable such that the speed and/or direction of rotation of the balance shaft may be varied.
The engine assembly may further comprise a variable speed transmission operatively disposed between the electric motor and the balance shaft. The variable speed transmission may be configured such that the speed and/or direction of rotation of the balance shaft may be varied, e.g. relative to a crank shaft of the engine. For example, in order to balance a different mode or order of vibration of the engine.
The balance shaft may be rotated at the same speed as the crank shaft or at twice the speed of the crank shaft. Alternatively, the balance shaft may be driven at half the speed of the crank shaft. Alternatively again, the balance shaft may be driven at any other fraction or multiple of the rotational speed of the crank shaft.
The speed and/or direction in which the balance shaft is rotated may be varied according to the displacement of the engine. The rotational speed and/or direction of the balance shaft may be varied according to the number of cylinders of the engine that are active.
The rotation of the balance shaft may be controlled in order to maintain a predetermined difference in phase angle between the balance shaft and a crank shaft of the engine. When the rotational speed of the balance shaft is not equal to the rotational speed of the crank shaft, rotation of the balance shaft may be controlled such that the difference in phase angle between the balance shaft and the crank shaft is equal to the predetermined difference each time the phase angle of the crank shaft is equal to 0 degrees, or another predetermined phase angle.
The assembly may further comprise a controller comprising one or more modules configured to control the operation of the engine, the electric motor, and/or the variable speed transmission.
The assembly may further comprise a further balance shaft comprising a further eccentric mass. The electric motor may be configured to selectively rotate the further balance shaft relative to the engine in order to balance the vibration characteristic of the engine, e.g. according to a vibration characteristic of the engine to be balanced.
The engine assembly may further comprise a further variable speed transmission operatively disposed between the electric motor and the further balance shaft. The further variable speed transmission may be configured such that the speed and/or direction of rotation of the further balance shaft may be varied.
The assembly may be configured to maintain a predetermined difference in phase angle between the balance shaft and the further balance shaft. The balance shaft and further balance shaft may be coupled, e.g. mechanically coupled. For example, the balance shaft and further balance shaft may be coupled by a gear or chain drive. Alternatively, the electric motor, variable speed transmission, and/or further variable speed transmission may be configured to maintain the predetermined difference in phase angle between the balance shaft and the further balance shaft.
The assembly may further comprise a coupling configured to selectively couple the electric motor to the balance shaft. For example, according to a running speed or displacement of the engine, e.g. according to the vibration characteristic of the engine to be balanced.
The assembly may further comprise a further coupling configured to selectively couple the electric motor to a crank shaft or transmission of the motor vehicle, e.g. in order to supplement the power provided by the engine.
The electric motor may be configured to receive power from the engine and/or a brake system of the vehicle and charge a battery of the vehicle. This may be known by those skilled in the art as regenerative braking.
The assembly may be configured such that rotation of the balance shaft is driven by the engine when the electric motor is charging the battery. For example, the balance shaft may be couplable to the crank shaft of the engine such that rotation of the balance shaft may be driven by the engine. Alternatively, the variable speed transmission, further variable speed transmission, and/or an additional transmission may be configured to selectively transmit power mechanically from the engine or transmission to rotate the balance shaft.
According to another aspect of the present disclosure, there is provided a method of operating an internal combustion engine assembly for a motor vehicle, wherein the engine assembly comprises an engine, an electric motor wherein the motor vehicle is a hybrid vehicle and wherein the electric motor forms part of a hybrid drive system of the vehicle, and a balance shaft comprising an eccentric mass, wherein the method comprises rotating the balance shaft using the electric motor in order to balance a vibration characteristic of the engine.
The method may further comprise selectively providing power to the hybrid drive system using the electric motor, e.g. supplementing the power from the internal combustion engine.
The electric motor may be a motor-generator provided within a hybrid drive system of the vehicle. The method may further comprise: receiving power from the engine or a brake system of the vehicle using the electric motor; and charging a battery of the hybrid vehicle using the electric motor.
The method may further comprise driving the rotation of the balance shaft using the engine whilst the battery is being charged. For example, the balance shaft may be coupled, e.g. mechanically coupled, to the crank shaft of the engine whist the electric motor is acting as a generator to charge the battery.
The method may further comprise: selectively using the electric motor to rotate the balance shaft when the electric motor is not providing power to the hybrid drive system.
The engine may comprise a variable displacement engine. The method may further comprise: varying the displacement of the engine, e.g. by deactivating one or more cylinders of the engine; and controlling the speed and/or direction of rotation of the balance shaft in order to balance the vibration characteristic of the engine.
For example, the engine assembly may comprise a variable speed transmission operatively disposed between the electric motor and the balance shaft. The variable speed transmission may be configured such that the speed and/or direction of rotation of the balance shaft may be varied relative to a crank shaft of the engine. The operation of the variable speed transmission may be adjusted in order to control the speed and/or direction of rotation of the balance shaft. For example, the direction in which the balance shaft is rotated may be reversed when one or more cylinders of the engine are deactivated or reactivated.
The speed and/or direction of rotation of the balance shaft may be controlled such that a different mode and/or order of vibration of the engine is balanced by the rotation of the balance shaft.
The method may comprise decoupling the electric motor from the balance shaft when the engine running speed is above a threshold running speed, e.g. such that the balance shaft is no longer rotated by the electric motor when the engine running speed is above the threshold running speed.
To avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the disclosure. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the present disclosure may also be used with any other aspect or embodiment of the disclosure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.